Bottomless portafilter advice for San Marino Compak CK

I tried purchasing a 58mm bottomless portafilter on Ebay supposedly for "E61" machines, but it turns out that its OD was 2.13mm to wide to fit into my groupe. The lugs were OK but the diameter was fractionally too big.

Since I live in a rural far north Qld. location and have to buy on the web, my question is, how can I choose a bottomless portafilter online that will fit my model HX machine without info on the OD from any of the online sellers? When I've purchased group head gaskets before they are just standard 72mmX56mmX8mm, so its just the seating ledge for the portafilter that seems to be the problem. I've added a photo for clarity. The measurement is close but not exact.

San Marino use a proprietary group head, similar to an E61 except for the collar dimensions as you have found out.

You will most likely have to buy a standard portafilter and then get someone with a metal lathe or holesaw to cut out the base.

Many thanks for the explanation. I thought the group dimensions conformed to a standard but obviously they don't. Coffee Parts used to once have the parts diagram for my model San Marino online, but alas, no more. I have pdf's of the parts list for my model [excluding the portafilter detail unfortunately], and also the one's you linked to on CoffeeParts, [many thanks for that link], but I think those listed are different from mine. Don't know if they would fit or not - or which one to choose if they did.